1. Field of the Invention
The present invention relates to an electromagnetic driving device for causing linear movement of a member to be driven. The electromagnetic driving device according to the present invention is used, for example, for a speedometer of an automobile, a tachometer of an automobile, a linear tracking arm of a record player for moving a tone arm, or a printer for printing characters.
2. Description of the Prior Art
In a conventional electromagnetic driving device for causing linear movement of a movable member, two bar-shaped fixed magnetic cores are arranged in parallel at a distance therebetween.
The movable member is located between the fixed magnetic cores and is capable of moving freely in the longitudinal direction. A coil is wound on one fixed magnetic core. A unidirectional magnetic field is formed between the fixed magnetic cores by the movable member. The movable member is moved in the longitudinal direction by the interaction between the unidirectional magnetic field and the current of the coil.
In order to increase the stroke, i.e., the range of movement, of the movable member while maintaining the same driving force, the cross-sectional area of the coil-wound fixed magnetic core must be increased in proportion to the increase in the length of the fixed magnetic core. The longer the fixed magnetic core, the greater the number of turns of the coil winding and, hence, the greater the magnetic flux. The increase of the cross-sectional area of the fixed magnetic core is therefore necessary to prevent magnetic flux saturation.
To double the stroke with the same driving force, therefore, it has thus been necessary to double both the length and the cross-sectional area of the fixed magnetic core, thereby increasing the weight of the fixed magnetic core four times. Thus, in the prior art, to increase the stroke of the movable member, one has had to chose between the disadvantage of a considerably increased weight of the fixed magnetic core or a reduction in the driving force.
An example of a prior art electromagnetic driving device for causing linear movement is disclosed in Japanese Unexamined Utility Model Publication (Kokai) No. 55-26414 of Yokogawa Denki Seisakusho, entitled "Linear Meter".